Question

Why does pcl5 exist as an ionic solid whereas pf5 exist as a covalent one?

Answer 1

Hello mate,

The type of bond formed depends on the chemical species involved in the bonding. In this case, phosphorus is the same in both cases, so the effect depends on the halogens. Comparing Cl and F in terms of atomic size, Cl is relatively larger than F (though the opposite is expected because F has more electrons, but nuclear charge is higher in F than Cl). hence, Cl has lower electron density, resulting into lower polarization hence the bond formed has more ionic character. On the other hand, F has higher charge density due to smaller atomic size, reulting into higher polarization thus the bond formed due to higher polarization normally has more covalent character than ionic.

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